good summary wendigo
you can't pillage before you stormed the fort or ?
i agree that getting attacked at 5 forts at the same time is bad . BUT it would be even worse if you had no castles around there because the 5 provinces would have been lost immediately + in mid / late game you probably have in most of them a temple anyway + pd which is lost immediately so - 300 gold or so .
with a fort you only need 1 point = 1 gold in defense in order to see the attacking force
and perhaps of the 5 besieged forts you can retaliate on 1 or 2 immediately and at the others the enemy marches further so no damage at all.
even if he besieges perhaps you are lucky and in one of them he doesn't break the walls at the first turn .
finally for blood nations it is especially important to castle . especially abysia can fly in a devil army quite early which has thnx to the demonbreed a range of 3
otherwise the valuable blood hunters would either be slain or if it is a weak attack like call of the wild , ghost riders .....
at least the blood slaves captured this turn are most likely wasted for battle spells like summon imps
so ihmo for blood hunting nations especially castling is a must while e.g. ulm may benefit more from not castling everything for better troop production ( at least early - midgame )